1. Field of the Invention
The invention relates to a voltage transformer for use with high voltages comprising an insulating body and a bushing laterally joined thereto. More particularly the invention relates to a voltage transformer of the aforesaid type in which the insulating body carries a high-potential winding which includes several serially connected subwindings which surround an iron core at spacings which increase in steps with the voltage, and which are connected with their outer winding end to a control electrode which extends into the bushing.
2. Description of the Prior Art
In one voltage transformer of this type, the insulating body carries individual coil forms which have cylindrical extensions for forming the bushing. The individual coil forms have on their outer as well as inner surfaces conductive coatings which are also provided on the inner and outer surfaces of the cylindrical extensions. Disposed on the individual coil forms are the subwindings forming the high-potential winding of the transformer. These subwindings are connected in series with each other by connecting the respective inner winding end of each subwinding to a coating on the coil form associated therewith, which coating, in turn, is connected to a conductive coating on the coil form of the subwinding of the next-higher voltage; the latter coating then being connected to the outer winding end of the subwinding of the next-higher voltage.
The above-described known voltage transformer has the disadvantage that it is complicated in design and therefore, expensive to manufacture. Moreover, it is further disadvantageous in that the conductive coatings on the coil forms and their interconnection with the subwindings results in an unfavorable surge voltage distribution.
In another known voltage transformer of the above-type, the high-voltage winding of the transformer comprises a number of series-connected subwindings with successively increasing diameters which are arranged axially side by side. The individual subwindings of the high-voltage winding are connected in series electrically by directly connecting the inner winding end of a subwinding to the outer winding end of the adjacent subwinding of the next-higher voltage. The individual subwindings are connected to each other mechanically by connecting straps, and the subwinding assembly so produced is held together by the innermost subwinding and the output lead of the outermost subwinding. The subwinding assembly is surrounded on the outside by a shielding cylinder which serves to control the voltage, and the indiviudual subwindings are impregnated with an impregnating resin. Moreover, SF.sub.6 is preferably used as the insulating medium for the high-voltage insulation of the transormer.
The aforesaid voltage transformer is also disadvantageous in that it is not very well suited for construction by plastic or casting-resin techniques. In particular, the shielding cylinder required for controlling the voltage impedes the shrinking of the casting resin. There is thus a danger that voids and cracks might be formed in the cast resin which would have an adverse effect of the high-voltage dielectric strength.
It is therefore an object of the present invention to provide a voltage transformer of the above-type which is relatively simple to manufacture and has a high dielectric surge voltage strength.